The invention relates generally to protection of switching devices, and more particularly, to protection of micro-electromechanical system based switching devices.
A circuit breaker is an electrical device designed to protect electrical equipment from damage caused by faults in a circuit. Traditionally, most conventional circuit breakers include bulky electromechanical switches. Unfortunately, these conventional circuit breakers are large in size thereby necessitating use of a large force to activate the switching mechanism. Accordingly, to employ electromechanical contactors in power system applications, it may be desirable to protect the contactor from damage by backing it up with a series device that is sufficiently fast acting to interrupt fault currents prior to the contactor opening at all values of current above the interrupting capacity of the contactor.
As an alternative to slow electromechanical switches, fast solid-state switches have been employed in high speed switching applications. As will be appreciated, these solid-state switches switch between a conducting state and a non-conducting state through controlled application of a voltage or bias. For example, by reverse biasing a solid-state switch, the switch may be transitioned into a non-conducting state. However, since solid-state switches do not create a physical gap between contacts when they are switched into a non-conducting state, they experience leakage current. Furthermore, solid-state switches are used in a combination of series parallel topology that includes one or more arrays of switches that facilitate higher voltage and current handling capabilities. However, the arrays of switches open or close asynchronously, resulting in an undesirable magnitude of load current flowing through the switches. Accordingly, the load current may exceed the current handling capabilities of the switches causing shorting or welding and rendering the switches inoperable. Therefore, there is a need for enhanced protection of such an array of switches.